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ERG/200806

A graphical technique for explaining the relationship between energy security and greenhouse gas emissions

Larry Hughes and Nikita Sheth

Energy Research Group Department of Electrical and Computer Engineering

Dalhousie University

1 September 2008

A graphical technique for explaining the relationship between energy security and greenhouse gas emissions

Larry Hughes and Nikita Sheth

Abstract

The need for energy security and the impact of anthropogenic climate change are expected to be two of the major challenges facing humanity in the twenty-first century. Despite their common root cause—humanity’s seemingly unquenchable demand for energy—the solutions to improving energy security and reducing greenhouse gas emissions are not necessarily compatible, since solving one may further exacerbate the other. The apparent lack of understanding and confusion over these two issues on the part of the general public, politicians, and policymakers suggests that there is a need to explain both the commonality and the differences between energy security and greenhouse gas emissions.

This paper presents a graphical technique for explaining this relationship, based upon jurisdiction-specific data on energy supply, infrastructure, affordability, greenhouse gas emission factors, and consumption. The jurisdiction’s energy sources are ranked using AHP (Analytic Hierarchy Process). The resulting security-emissions graphs allow the viewer to understand the state of a jurisdiction’s energy security, the level of greenhouse gas emissions, and the effort needed to improve energy security and reduce emissions.

Keywords: Analytic Hierarchy Process, Energy Security, Climate Change

1 Introduction

It is generally accepted that the world’s population is facing two separate but interrelated

energy challenges. One of these is the build-up of atmospheric greenhouse gases—

predominantly carbon dioxide—caused in part by the anthropogenic combustion of fossil

energy sources, notably coal, oil, and natural gas (IPCC, 2001). The other, energy security, or

simply security of supply, is being driven by price increases and production challenges of these

and other energy sources (Yergin, 2006).

Solutions to these challenges can be classified into one of two common approaches (Hughes,

2007). The first, energy reduction, consists of policies that lead to a measureable reduction in

the consumption of energy for a given activity. Energy reduction policies, from improved

building codes to limiting highway speeds, can help address energy security and greenhouse gas

issues. The second, energy replacement, are those policies intended to encourage replacing

one energy source with another.

Hughes, Seth: Energy security and climate change 2

However, unlike energy reduction, some strategies for replacing one energy source with

another are not necessarily applicable to both reducing greenhouse gases and improving

energy security. For example, a jurisdiction could cut its greenhouse gas emissions by phasing

out its use of coal for electrical generation, but the economic and social effects could be

devastating without finding a secure energy source that could replace the electricity generated

from coal. Similarly, improving a jurisdiction’s energy security through increased consumption

of secure sources of fossil energy can exacerbate the anthropogenic emissions of greenhouse

gases.

With the 2010-12 Kyoto deadline rapidly approaching and energy security becoming a major

issue in many countries, there is a need for techniques to explain the similarities, differences,

impacts, and potential solutions to these two challenges. This paper presents a graphical

technique for illustrating the relationship between energy security and greenhouse gas

emissions within a jurisdiction.

To develop a security-emissions graph, two sets of jurisdictional-specific data are required: the

levels of consumption of each type of energy known to be used in the jurisdiction and the

greenhouse gas emissions associated with each of the energy sources. Determining how secure

each energy source can be more subjective, requiring a detailed understanding of the state of

supply, infrastructure, and affordability of the different energy sources. In this paper, a

decision support tool, Analytic Hierarchy Process (or AHP), is employed to rank each energy

sources in terms of its contribution to the energy security of a jurisdiction.

The remainder of the paper is organized as follows. The next section discusses energy-related

greenhouse gas data and emissions factors. The third section describes how AHP can be

employed to rank different energy sources in terms of their contributions to a jurisdiction’s

energy security. The graphical technique and its interpretation are presented in the fourth

section, while the fifth section describes the software developed to generate security-emissions

graphs. The paper is concluded with a discussion of our experiences presenting the security-

emission graphs to the general public and policy makers.


2 Emissions factors

There is a mounting body of evidence that increasing concentrations of atmospheric

greenhouse gases from energy-related activities are changing the planet’s climate (IPCC, 2001).

Most, if not all, energy sources contribute in some way to greenhouse gas emissions; for

example, the combustion of fossil fuels, the energy needed to mine and process uranium ore,

fugitive emissions from coal, hydroelectricity, or natural gas, and the energy required to build

generating stations or manufacture wind turbines and photovoltaic panels.

Although the principal anthropogenic greenhouse gas is carbon dioxide (CO2), there are other

energy-related greenhouse gases, notably methane (CH4) and nitrous oxide (N2O). All of these

gases have the ability to trap heat in the atmosphere; their individual strengths, relative to CO2,

are described in terms of their global warming potential or GWP (IPCC, 2001). Since the

emissions from an energy source can be more than simply CO2, they are often expressed as

CO2-equivalents or CO2e, the sum of the masses and GWPs of the different gases it emits (for

example, see (Environment Canada, 2007)).

An energy source’s impact on the climate can be expressed in terms of its greenhouse gas

emissions factor, in this case, the volume of greenhouse gases emitted per unit of energy

consumed; for example, tonnes of CO2e per MWhel or kilograms of CO2e per litre of fuel. The

value of the emissions factor will depend upon what is deemed to constitute the emissions

associated with the energy source, which can include any production, extraction, distribution,

and combustion related emissions. To avoid misinterpretation of the results or suggestions of

bias, all energy sources should be subject to the same analysis. To compare different energy

sources, the individual intensities can be normalized to a common emissions factor, for

example, kilograms of CO2e per gigajoule.

For most energy sources, there is little dispute over the associated greenhouse gas emissions as

they can be obtained empirically or theoretically. However, sources such as nuclear or

renewables can be problematic, for although they appear to have no emissions, there are

related emissions. In the case of nuclear, parts of the nuclear fuel cycle, notably mining and

reprocessing, can be CO2-intensive, while with hydroelectricity, the decomposing of vegetation


in the reservoir can produce CH4. Although the energy produced by renewables such as wind

and solar is considered emissions-free, the energy used in the manufacture of the equipment

(i.e., the embedded energy) can be associated with CO2 emissions using full-energy chain

analysis or FENCH (van de Vate, 1997).

3 Energy security

The state of energy security in a jurisdiction is dictated by its energy supplies, the cost of these

supplies, and the infrastructure required for producing, distributing, and possibly storing the

energy for the consumer. The relationship between supply and infrastructure leads to two

corollaries. First, the lack of infrastructure will exclude the consumer from accessing those

forms of energy that rely on the infrastructure, and second, the lack of affordable supply,

regardless of the availability of infrastructure, will mean the consumer is unable to benefit from

that energy source.

Determining the influence of an energy source on the energy security of a jurisdiction can be

more subjective and not as easily quantifiable as determining the greenhouse gas emissions

factor associated with the energy source. In its simplest form, an energy source can be

classified as either “secure” or “insecure”; however, this distinction can be seen as arbitrary and

without merit or basis. It also may hide the fact that energy sources can have “shades” of

security, with some sources being more secure than others. Any methodology chosen to rank

an energy source in terms of a jurisdiction’s energy security must be justifiable and should not

be jurisdiction-specific.

The methodology employed here is the Analytic Hierarchy Process (AHP), a decision analysis

tool that accounts for quantitative as well as qualitative aspects of a decision problem.

3.1 Analytic Hierarchy Process

The Analytic Hierarchy Process or AHP is a multi-criteria decision analysis technique commonly

used for energy and environmental modeling (Saaty & Alexander, 1989; Zhou, Ang, & Poh,

2006). For example, Kagazyo et al. (1997) used AHP to evaluate and prioritize energy-related

research projects in Japan, in less developed countries, and in the world as a whole. Poh and

Ang (1999) carried out a study of alternative fuels for land transportation in Singapore. Kablan


(2004) presented an AHP based framework for the prioritization of energy conservation policy

instruments in Jordan, while Elkarmi and Mustafa (1993) used AHP to select the best policies

for increasing the utilization of solar energy technologies in Jordan.

AHP decomposes a decision problem into a hierarchical structure consisting of at least three

levels: the objective, the main criteria, and the alternatives; one or more intermediate levels for

sub-criteria can be added if and when required (Saaty, 1980). The following are the three levels

of the decision hierarchy used to rank the energy sources in terms of energy security.

3.1.1 The Objective

AHP is to evaluate the different energy alternatives available to a jurisdiction and from this,

rank their contribution to the jurisdiction’s energy security. The objective is therefore “energy

security”. Applying AHP to the criteria and alternatives will result in the ranking of each energy

source, in terms of energy security, for the jurisdiction’s energy portfolio.

3.1.2 The Criteria

The second level, the main criteria, must be broad enough to encompass all aspects of energy

security. For the proposed methodology, the IEA’s definition of energy security is used, notably

the reliable supply of energy at an affordable price (IEA, 2001; Constantini, 2007). This

definition suggests that energy security depends upon two criteria: supply and affordability.

However, given the energy security corollaries discussed above, the supply criteria is further

decomposed into supply and infrastructure. No sub-criteria are used.

The following guidelines are recommended when examining each of the energy security

criteria:

Supply. The ranking of supply should be based upon the importance attached to the quality

of a given energy source, what is known about the reliability of the supplier(s), and the state

of the resource. If supplies are problematic, it is necessary to include the possibility of

alternative suppliers. Supply can be discussed in terms of present or future possible

supplies—the timeline is chosen must be applied to all criteria consistently. The quantity of

supply is not considered here, as it is addressed later.


Infrastructure. Infrastructure ranking should focus on the significance placed upon the

resilience, age, quantity, and accessibility of the infrastructure. The infrastructure to be

considered is that found within the jurisdiction and refers to anything that moves energy

from the point of production to the point of consumption; this can include loading depots,

pipelines, roadways, transmission grids, railways, and fuel tankers. The infrastructure

outside the jurisdiction’s boundary is treated as part of supply.

Affordability. Affordability refers to the cost of an energy source and can be interpreted in

a number of different ways; two frequently used are the cost per unit energy and the

impact on the jurisdiction or end-user. In jurisdictions where energy is subsidized, the

affordability can be considered less of an issue to the consumer; however, since it can

become an issue to those generating the subsidies, it should be considered in the

comparison.

3.1.3 Alternatives

The third (and final) level consists of the alternatives, that is, the different energy sources

available to the jurisdiction. The choice of energy sources are at the discretion of the user and

will vary from jurisdiction to jurisdiction.

3.1.4 Obtaining the ranking

Once the decision hierarchy is formed, pair-wise comparisons are performed at each level to

determine the weights of the different criteria and alternatives. First, the different main

criteria are compared, in pairs, with respect to the objective. This is followed by pair-wise

comparisons of the alternatives with respect to each criterion. As a result of these pair-wise

comparisons priorities (or weights) will be obtained for each criterion and alternative. AHP then

takes the priorities of the criteria and the alternatives to produce the final ranking of the energy

sources. The ranking refers to the contribution of each energy source to the energy security of

the jurisdiction.

4 Creating a security-emissions graph

Creating an energy security-climate change graph is a three step process. The first step involves

obtaining the emissions factors for each energy source used in the jurisdiction. The second step


requires the different energy sources to be ranked by AHP to determine their energy security

index. The final step creates the graph by plotting each energy source in terms of its energy

security index and associated emissions. The following example shows how security-emissions

graph can be created.

The jurisdiction used in this example is Nova Scotia, a small province of about one million

people on Canada’s Atlantic coast. Table 1 lists Nova Scotia’s portfolio of primary energy

sources and associated energy suppliers. From the table, it is clear that Nova Scotia relies

almost exclusively on imported energy sources.

Table 1: Nova Scotia’s energy portfolio (Hughes, 2007)

Source Demand Supplier

Refined petroleum products (oil)

178.3 PJ 63.1% North Sea, Venezuela, Middle East, Newfoundland, U.S.

Coal (imported) 69.1 PJ 24.5% Colombia, Venezuela, U.S.

Renewables (non-utility) 16.6 PJ 5.9% Nova Scotia

Coal (domestic) 10.3 PJ 3.7% Nova Scotia

Primary electricity 2.7 PJ 1.0% Nova Scotia

Natural gas 5.4 PJ 1.9% Nova Scotia

Total 282.4 PJ 100.0%

4.1 Emissions factors

The first step in creating the graph is to determine the emissions factors for the fuels used in

the jurisdiction. The emissions factors for Nova Scotia are shown in Table 2.

Table 2: Nova Scotia’s normalized emission factors

Source Emission factor Multiplier Normalized kg CO2/GJ

Refined petroleum products (oil)1 2.5 kg CO2/l 0.035 GJ/l 71.4

Coal (imported)1 2.288 kg CO2/kg 0.0277 GJ/kg 82.6

Renewables (non-utility)2 31 kg CO2/MWh 3.6 GJ/MWh 8.6

Coal (domestic)1 2.249 kg CO2/kg 0.0277 GJ/kg 81.2

Primary electricity (hydroelectric)2 16 kg CO2/MWh 3.6 GJ/MWh 4.4

Natural gas1 1.891 kg CO2/m3 0.0371 GJ/m3 50.9

1 Emission factor from (Environment Canada, 2007) and multiplier from (NEB, 1999)

2 Emission factor and multiplier from (van de Vate, 1997)


4.2 Calculating energy security index for different energy sources

The energy sources are then ranked in terms of their energy security index using AHP. In this

example, five regional energy analysts were contacted and their responses to the AHP energy

security survey for Nova Scotia were obtained. The results of the main criterion rankings are

shown in Table 3, with supply being the most important and affordability the least.

Table 3: Ranking of main criterion

Supply Infrastructure Affordability

0.51 0.31 0.18

The pair-wise comparisons were then performed for the energy sources with respect to each of

the three criteria. The total consumption associated with each energy source was ignored

during the ranking process. The rankings are shown in Table 4.

Table 4: Ranking of alternatives with respect to each of the main criterion

Source Supply Infrastructure Affordability

Oil 0.08 0.17 0.09

Domestic coal 0.25 0.12 0.20

Imported coal 0.11 0.17 0.15

Natural gas 0.09 0.09 0.10

Hydro 0.28 0.28 0.32

Renewables (non-utility) 0.19 0.17 0.13

The final step is the calculation of the energy security index (i.e., ranking) for each energy

source. In this example, hydroelectricity was considered the most secure, followed by domestic

coal, and non-utility renewables. Oil had a low ranking because only a small portion is from

Canadian sources (from Newfoundland and Labrador), while natural gas has limited

infrastructure in Nova Scotia and supply is in decline (NEB, 2007).


Table 5: Energy security index for the energy sources

Source Index

Oil 0.11

Domestic coal 0.20

Imported coal 0.14

Natural gas 0.09

Hydro 0.29

Renewables 0.18

4.3 Creating the security-emissions graph

The energy security index, the emissions factor, and the consumption values for the different

energy sources available to the jurisdiction can be represented in a tabular format, such as that

shown in Table 6.

Table 6: Energy data for a sample jurisdiction

Energy Source Security

index Emissions factor

(kg CO2/GJ) Consumption

(PJ)

Oil 0.11 690 178

Domestic coal 0.20 940 10

Imported coal 0.14 940 69

Natural gas 0.09 460 5

Hydro 0.29 16 3

Renewables 0.18 30 17

The values of the security index and emissions associated with each energy source can be

plotted as a series of data-points on an X-Y graph. Together, these give an indication as to the

position of each energy source, relative to the other energy sources in terms of their security

and emissions. The graph for the data in Table 6 is shown in Figure 1.


Figure 1: Graph of energy security index vs. emissions factor In this figure, the horizontal axis represents the energy security index, running from least secure

(left) to more secure (right). The vertical axis represents the emissions factor, running from

high-intensity CO2e sources (bottom) to low-intensity CO2e sources (top).

Energy sources found towards the upper-right region of the graph can be more secure and less

carbon-intensive than those found elsewhere in the graph. These energy sources can include,

for example, nuclear, hydroelectric, biomass, wind, solar PV, and solar thermal. Depending

upon the state of the resource, it can also include natural gas.

On the other hand, energy sources found more towards the lower-left region of the graph are

typically less secure and more carbon-intensive than those found elsewhere in the graph.

Energy sources in this region are the least desirable for the jurisdiction in that they are both less

secure and high-carbon emitters. Sources can become more insecure and higher-carbon

emitters as they move further to the bottom-left; for example, shifting from imported oil to

imported coal.

The graph, as it now stands, shows the relative positions of the different energy sources, but

gives no indication as to the jurisdiction’s reliance on each source. This can be achieved by

making the size of each data point represent the consumption of that particular energy source.

Figure 2 shows the effect of adding consumption to the graph; here, the size of each circle

Oil

Domestic coalImported coal

Natural gas

HydroRenewables

0

10

20

30

40

50

60

70

80

90

0.000 0.050 0.100 0.150 0.200 0.250 0.300

CO

2e

inte

nsi

ty (

kg/G

J)

Energy security index


represents of the total consumption of the energy source in the jurisdiction (the actual

consumption, expressed in petajoules has been included with the name of each energy source).

Figure 2: A security-emissions graph for Nova Scotia The security-emissions graph shows how reliant the jurisdiction is on CO2-intensive energy

sources and the relative security of each energy source. It also shows the magnitude of each

energy source and, by extension, where the jurisdiction should put its efforts in addressing

improving security, reducing emissions, or both.

Ideally, a jurisdiction’s replacement strategies should be moving energy supply towards the

more-secure, low-carbon region of the graph. However, with the widespread availability of

coal, many jurisdictions are either already in or shifting into the more-secure, high-carbon area

of the graph. Jurisdictions that are relying on greater quantities of imported coal are staying in

the less-secure, high-carbon region.

5 Examples

As discussed earlier, security-emissions graphs can be applied to jurisdictions. They can also be

applied to energy suppliers. This section gives examples of each.

An example of a security-emissions graph is shown for Canada in Figure 3.

Oil178PJ Domestic coal

10PJImported coal

69PJ

Natural gas 5PJ

Hydro3PJ

Renewables17PJ

0

10

20

30

40

50

60

70

80

90

100

0.000 0.050 0.100 0.150 0.200 0.250 0.300

CO

2e in

ten

sity

(kg

/GJ)



Figure 3: A security-emissions graph for Canada (IEA, 2007) The security index values were determined by the authors using the known state of the supply,

infrastructure, and affordability of the different energy sources. This meant that, for example,

domestic natural gas had a lower security rating than domestic crude because of natural gas

reserves are in decline, whereas crude oil reserves (both conventional and tar sands) are

forecast to experience a slight growth over the next decade. Similarly, nuclear does not have a

high security index value as part of Canada’s nuclear fleet is being decommissioned. The graph

suggests that as a nation, Canada is relatively secure in terms of its energy supply and meets

much of its energy demand from sources that have low emissions factors. Despite this, since

energy supplies and infrastructure are not uniformly distributed across the country, some

regions, such as the province of Nova Scotia, have limited energy security and are major

emitters of greenhouse gases, as shown in Figure 2 (above).

Security-emissions graphs need not be restricted to jurisdictions. In Figure 4, the authors have

constructed a security-emissions graph for NSP, a vertically-integrated electricity supplier in the

province of Nova Scotia.

CoalDomestic

17Mtoe

CoalImport

12Mtoe

CrudeDomestic

62MtoeCrudeImported

47Mtoe NatgasDomestic

69Mtoe

NatgasImported

9Mtoe

Nuclear24Mtoe

Hydro29Mtoe

Renewables12Mtoe

-10

0

10

20

30

40

50

60

70

80

90

100

110

0.000 0.050 0.100 0.150 0.200

Emis

sio

ns

fact

or

(kg

CO

2/G

J)



Figure 4: A security-emissions graph for NSP (Emera, 2007) The graph shows that NSP’s reliance on imported coal and (imported) petcoke make it energy

insecure and are both significant contributors the company’s greenhouse gas emissions. NSP’s

energy insecurity has been highlighted twice over the past three years, first with the loss of

petcoke supplies from the US Gulf coast refineries after Hurricane Katrina, and more recently

with the Venezuelan state-owned coal company, Carbozulia, notice to NSP that it is

“suspending 2008 shipments pending a review of the contract” (Emera, 2008).

6 Software implementation

A software tool has been developed in VBA and Excel by the authors to both the energy

security index and the graph for a given set of input data.

There are five distinct steps in the implementation. First, the user is expected to list the names

of the jurisdiction’s energy portfolio, the emissions factor, and the consumption associated with

each energy source. Second, the user performs a pair-wise comparison of the main criteria

(supply, infrastructure, and affordability), from this, the software generates the ranking of the

criteria. In the third step, the rankings of the different energy types (the alternatives) are

determined for each of the main criteria from the user-supplied pair-wise comparisons of all

the energy types. Fourth, the final rankings of each energy type are calculated from the

rankings of the main criteria and the rankings of the different energy types. In the final step,

CoalImported

5,097 GWh

CoalDomestic

1,439 GWh

Petcoke2,592 GWh

Natgas390 GWh

Oil431 GWh

Renewables998 GWh

Purchases405 GWh

-200

0

200

400

600

800

1000

1200

0.000 0.050 0.100 0.150 0.200 0.250 0.300

Emis

sio

ns

fact

or

(kg

CO

2/M

Wh

)



the security-emissions graph is generated from the supplied emissions factor, the consumption

data, and the security ranking of each energy type. Any step can be repeated as required.

Copies of the software and instructions on its operation can be obtained by contacting the

authors.

7 Concluding remarks

Humanity’s seemingly unquenchable demand for energy is manifesting itself, both directly and

indirectly, in a number of different ways: food shortages, energy shortages, rising energy prices,

and increasing levels of greenhouse gases. Regardless of the issue, most, if not all, of them can

be traced back to the need for energy security—the reliable supply of energy at an affordable

price.

The apparent lack of understanding and confusion on the part of the general public, politicians,

and policymakers over both the commonality and the differences between energy security and

climate change motivated this work. The graphical technique developed in this paper offers a

clear and understandable way of explaining this relationship for any jurisdiction, using both

quantitative (greenhouse gas emissions factors and energy consumption) and qualitative

(security of supply) data. The resulting security-emissions graphs allow the viewer to

understand the state of a jurisdiction’s energy security, its greenhouse gas emissions factor,

and the consumption of each fuel source. It also allows the viewer to appreciate the effort

needed to improve energy security, reduce emissions, and change consumption habits.

Ranking a jurisdiction’s energy portfolio is probably the most challenging component of the

graphs. AHP offers a straightforward and reasonable approach to determining the rankings of

the criteria and the alternatives.

The availability of a software tool that implements the AHP algorithms for up to 15 energy

alternatives and then generates the associated security-emissions graph is both a time-saver

and allows “what-if” type questions to be answered.

The authors have been using security-emissions graphs to describe the state of Nova Scotia’s

and Canada’s energy security to various groups and organizations since late 2007. Our

experience with presenting the graphs at public events has been that they are easily explained


and understood. It has raised awareness of the security of Nova Scotia’s energy portfolio, the

impact of these sources on the climate, and the challenges associated with becoming more

secure and reducing greenhouse gas emissions.

8 Acknowledgements

The authors would like to acknowledge the assistance of other members of the Energy

Research Group during the testing of the security-emissions software.

9 Bibliography

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Hughes, L. (2007). Energy Security in Nova Scotia. Ottawa: Canadian Centre for Policy Alternatives.

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IEA. (2001). Toward a sustainable energy future. Paris: International Energy Agency.

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Poh K.L., A. B. (1999). Transportation fuels and policy for Singapore: an AHP planning approach. 37 (3).

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Saaty, T., & Alexander, J. (1989). Conflict Resolution:The Analytic Hierarchy Process. Praeger.

van de Vate, J. F. (1997). Comparison of energy sources in terms of their full energy chain emission factors of greenhouse gases. 25 (1), pp. 1-6.

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Zhou, P., Ang, B., & Poh, K. (2006). Decision analysis in energy and environmental modeling: An update. Energy , pp. 2604-2622.

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